The present invention relates to spacer strips, more specifically to spacer strips used for constructing electrically heated mats. The present invention also relates to a method for economically manufacturing such spacer strips.
German Pat. Application No. P 21 27 567 (laid open on December 14, 1972) discloses electrically heated mats or rather structural elements for the production of such mats. These known mats comprise electrical heating elements in the form of meandering heating loops having legs arranged in parallel to each other wherein these legs are secured to cross bars extending at right angles relative to the longitudinal length of the heating loops. In this fashion, the heating loops and the cross bars form together a grid type mat which may be installed as desired.
The prior art mats as described above permit their production in any desired shape due to said cross bars. Further, the final assembly of the mats, that is, the insertion of the heating conductors into the cross bars may be done depending on the particular circumstances. In other words, the complete mats may be assembled in the work shop, especially where relatively simple heating surfaces are involved. On the other hand, the cross bars also permit an assembly at the construction site, especially where more involved surfaces are to be covered with these heating mats as is frequently the case in hospital rooms or the like.
In addition to the advantage of allowing for the formation of any desired shapes, the heating mats according to the prior art have other advantages. They are easily transported because they may be rolled up or plugged together and so forth. These mats further avoid separating layers in the flooring plaster due to the large mesh grid formation. This feature has the further advantage that the mats may be installed in a single work process.
In a further prior art embodiment means are provided for relieving the heating conductors from a bearing function within the grid arrangement. This relief is accomplished in that the cross bars which secure the heating conductors in position are interconnected with each other by spacing lands extending in the longitudinal direction of the mat or rather in the direction of the heating conductors.
Due to this feature of the prior art heating mats, it is possible to pre-assemble the grid in such a manner that it may be rolled up and that the grid may be cut with due regard to the area to be heated whereupon the heating conductors are simply pressed into the holding means of the cross bars in order to secure the heating conductors in accordance with the shape of the area to be heated. The holding means of the cross bars are arranged at relatively close but equal spacings, whereby sufficient flexibility is provided for rerouting the heating conductors in order to make necessary openings, for instance for wash stands, toilet bowl areas and the like, without causing an unpermissible heat density or heat congestions.
In addition to the above described prior art heating mats, comprising in the one system interconnecting cross bars and in the other system such cross bars in combination with longitudinally interconnecting lands, there are known grid-shaped heating mats wherein the heating conductors are mounted to concrete reinforcing steel grids. In addition, there are known area heating means such as heating pads and electric blankets, wherein the heating conductors are embedded in rather pliable materials such as fabrics or the like.
From the above description of the prior art it is apparent that the cross bars with their holding means for securing the heating conductors or resistors and their structural features are critical for the technical and economical characteristics of the above described two prior art systems. Thus, there is known a first type of cross bars in which the heating resistors or elements are secured in equally spaced slots provided in band or strip material arranged in an upright position, whereby said slots are self-locking. In a second type of cross bars the band or strip material is also provided with slots, however the slots are not self-locking and therefore U-shaped clamping members are used to cover the slots. In a third embodiment the cross bars also comprise a band or strip material, however, in this arrangement the band or strip material is maintained in a flat position and provided with equally spaced three-sided incisions which are preferably located in the center of the flat strip material, whereby tongues are formed which correspond to the cross section of the cable or heating conductor. The just described three basic arrangements may, of course, be modified in many different ways. In any event, the first and second type described above have the disadvantage that their use requires a relatively plain surface for the installation. Further, where spacing lands are employed they must be provided with plug incisions, whereby the whole system is weakened unless additional rather costly connecting means are employed, for example, along the angled butt connections, by means of welding or gluing, whereby the welding would involve a fillet weld or joint.
The third type of interconnection described above has the disadvantage that the making of said incisions also involves a rather technical effort, whereby the formation of said tongues usually requires the application of heat.